1. Field of the Invention
The invention disclosed in this patent pertains to check valves and stop/check valves for controlling the flow of fluid. Under conditions where the fluid is pulsating and flowing at a relatively low volume, a disc inside the valve tends to vibrate and strike against the valve seat. The invention incorporates into such valves a means for changing the path of flow of fluid which is pulsating and flowing at a relatively low volume so as to reduce vibration of the disc, and to prevent the disc from striking the valve seat.
2. Description of the Related Art
Valves are used to control the flow of fluids in various systems. For instance, stop valves, check valves and stop/check valves are often used to control refrigerants circulated under high pressure in refrigeration systems. A typical stop valve controls flow by being manually turned to the fully closed position which stops the flow of fluid, or fully opened position to permit maximum flow through the valve, or an intermediate position to regulate the flow. Check valves permit flow in only one direction and are used in lines where reverse flow is undesireable. When the fluid flows in the desired direction, a check valve utilizes the pressure drop across the valve to automatically open to permit the flow of fluid, but if the fluid stops or reverses direction the valve closes to prevent backwash. A stop/check valve combines the function of both a stop valve and check valve. A typical stop/check valve can be manually turned to a closed position to stop all flow of fluid, or turned to an open position whereby it automatically opens when the fluid flows in the desired direction and closes when the fluid stops or reverses to prevent backwash.
Check valves and stop/check valves rely on a sufficient fluid flow to open the valve. A pulsating, low-volume flow of fluid through a check valve or stop/check valve, however, will cause a disc within the valve to vibrate and strike the valve seat in response to the pulsation, causing unusually loud noise and, more seriously, damage to the valve.
A conventional stop/check valve typically comprises a valve housing having a fluid inlet port, fluid outlet port, valve seat between the two ports, and an inner wall between the valve seat and outlet port. Within the valve housing is a cylindrical metal valve disc which moves axially toward and away from the valve seat between closed and open positions, respectively. The means for moving the valve disc between open and closed positions typically comprises a rotatable valve stem which extends through an opening in the valve housing down to the valve disc. The lower end of the valve stem is connected to the valve disc in a manner which permits the valve disc to rotate and slide with respect to the valve stem. This type of rotatable, slidable connection can be made by a protuberance on the lower end of the valve stem which is inserted into a recess in the upper side of the valve disc and secured by a retaining ring fastened to the valve disc.
In one type of stop/check valve, the valve disc has an annular groove formed around the outer periphery of its lower side and a seal ring is disposed in the groove. The seal ring is held in the groove by a smaller-diameter circular metal retainer plate which is fastened to the lower side of the valve disc and presses against the front side of the seal ring.
To close the stop/check valve, the valve stem is rotated to move the valve disc toward the valve seat until the seal ring bears against the surface of the valve seat. The ability of the valve disc to rotate with respect to the valve stem allows the seal ring to engage and disengage the valve seat without scraping along the surface of the valve seat, which could damage the seal ring. To open a stop/check valve, the valve stem is rotated so that it moves in a direction away from the valve seat. With the valve stem having been turned to the open status, a sufficient amount of fluid flowing in a direction from the inlet port to the outlet port will cause the valve disc to slide axially up the valve stem, disengaging the seal ring from the valve seat and creating an opening or passage for fluid to flow past the outer edge of the seal ring and between the valve seat and the valve disc. If the flow stops, reverse flow and gravity will slide the valve disc down the valve stem thus closing the passage and checking the flow of fluid.
A stop/check valve of this type is used, for example, in large refrigeration systems with multi-cylinder compressors, which are often provided with a capacity reduction mode. When starting or shutting down a multi-cylinder compressor, it is typically necessary to reduce capacity down from, for example, eight cylinders to two cylinders. Some operating conditions require continuous operations at reduced capacity. When the compressor is running on all eight cylinders the fluid flows at a relatively high velocity and pressure and the pulsating effect of the flow is negligible. Reducing capacity down to two cylinders means the fluid is now circulated by the alternating discharge of just those two cylinders. The discharge of the two cylinders causes the fluid to pulsate in rhythm with the discharge of each cylinder, which in turn causes the slidable valve disc to pulsate or vibrate with the flow. In other words, the pulsating low volume flow of fluid causes the valve disc to slide up and down the valve stem and bang against the valve seat. Such a pulsation of flow and resulting vibration of the valve disc is often the cause of a ringing or chatter noise in a refrigeration system, and on occasion can be quite loud. The vibrating valve disc can cause undue wear and damage to the seal ring, valve seat, valve disc or possibly other parts of the valve. Vibration of the valve disc may even contribute to the problem of fluid leakage between the seal ring and valve disc, even when the valve is closed. Pulsation of the fluid causes the same type of vibration, noise and damage in a check valve.